Where do namespaces come from?

[forddavis]

Hello,

I have never previously used any namespace other than std, however I have been reading about them and I don't understand where they come from. Everywhere I read about them there is no mention of how the compiler gets them. Does a namespace need to be defined in a separate file or does the compiler already have them? If so how would I go about using say my computer science professor's namespace? It seems he just includes it in his code and expects us to use it, but I don't see how the compiler would automatically be familiar with the namespace.

Thanks in advance

[manasij7479]

To use the classes and functions declared in that namespace,
You need to include the header file where he used it.
and then attach a prefix:
your_profs_ns::
to the stuff declared there.

[Disch]

You define namespaces like this:

namespace myns
{
void SomeFunction();
}

// then you can use the namespace:

int main()
{
  myns::SomeFunction();

  // or if you prefer
  using namespace myns;
  SomeFunction();
}